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This Week in Science

Altitude Sickness

CREDIT: SIRAJ ET AL.

Whether the incidence of malaria will be (or has been) affected by the warming climate is poorly resolved. Global-scale analyses are fraught with technical difficulties, including problems with separating out changes resulting from destruction of mosquito habitat, insecticide use, and antimalarial drug use from multidecadal trends in climate change. Siraj et al. (p. 1154) performed parallel analyses of highland malaria in Ethiopia and Colombia to ask whether interannual changes in temperature could explain variation in malaria incidence with altitude. Modeling the data confirmed that malaria moves up in elevation in warmer years and allowed estimates of how many more millions of cases could be expected in tropical highland areas if the mean temperature increased by 1° to 3°C.

A Soft Molecular Spring

In noncontact atomic force microscopy, extremely high resolution has been achieved by attaching a terminal CO molecule to the metal scanning probe tip. This CO molecule can undergo torsional vibrations, and a full understanding of the imaging mechanism requires a measure of this spring constant. Weymouth et al. (p. 1120, published online 6 February; see the Perspective by Salmeron) used lateral force microscopy, in which the tip vibrates laterally across the surface, to determine this torsional constant. The stiffness of the isolated CO molecules on the tip was much less than that for CO molecules adsorbed on planar surfaces.

Nanoimaged Polaritons

Engineered heterostructures consisting of thin, weakly bound layers can exhibit many attractive electronic properties. Dai et al. (p. 1125) used infrared nanoimaging on the surface of hexagonal boron nitride crystals to detect phonon polaritons, collective modes that originate in the coupling of photons to optical phonons. The findings reveal the dependence of the polariton wavelength and dispersion on the thickness of the material down to just a few atomic layers.

Limited Stability

Deep ocean circulation is thought to be stable during warm, interglacial periods. Galaasen et al. (p. 1129, published online 20 February) constructed a highly resolved record of North Atlantic Deep Water production during the last interglacial period, around 128,000 to 116,000 years ago. The findings reveal large, centennial-scale reductions—in contrast to the prevailing paradigm. These changes occurred in an ocean warmer than that of today, but in a temperature regime similar to that expected because of global warming, raising the possibility that future ocean circulation, regional climate, and CO2 sequestration pathways could be impacted.

Crossing the Membrane

Adenosine triphosphate (ATP)–binding cassette (ABC) transporters couple ATP hydrolysis to the translocation of a wide variety of substrates across cell membranes. Srinivasan et al. (p. 1137) describe the structure of a yeast mitochondrial transporter involved in Fe-S protein biogenesis. The structure reveals bound glutathione, which suggests that glutathione is part of the translocated substrate. J. Y. Lee et al. (p. 1133) describe the structure of a bacterial ABC transporter that confers protection against silver and mercury. This protein also binds glutathione derivatives. The structure provides insight into how ligand interactions are coupled to ATP hydrolysis.

Evolutionary Duality

When ecological divergence involves traits that also contribute to mating behavior, such divergence could lead to rapid reproductive isolation and speciation. However, there are very few experimental demonstrations of such “dual” traits. Chung et al. (p. 1148, published online 13 February) now demonstrate that specific cuticular hydrocarbons are a dual trait that affects both desiccation resistance and mate choice in the widely distributed Australian species Drosophila serrata. These compounds have largely been lost from its rainforest-restricted, desiccation-sensitive, closely related sibling D. birchii.

Carbapenems Through the Looking Glass

The carbapenem class of antibiotics is a critical weapon in the ongoing fight against drug-resistant bacteria. Microbial biosynthesis of these compounds, which contain a strained β-lactam ring motif, proceeds via a precursor that has the wrong configuration at one of the ring carbons. Chang et al. (p. 1140) combined x-ray crystallography with multiple spectroscopic probes to map out the mechanism by which the CarC enzyme inverts the precursor configuration to its mirror image.

Persistent Plume

CREDIT: WALSH ET AL.

Energy from the solar wind is carried into Earth's magnetosphere and ionosphere through the reconnection of magnetic lines. When this coupling is strong, changes in the solar wind cause geomagnetic storms that perturb the magnetosphere and allow a plume of cool plasma to be released outward. As the plume rises from the ionosphere, it extends the boundary of its plasmasphere origin toward the magnetopause. Using simultaneous ground-based and satellite observations, Walsh et al. (p. 1122; see the Perspective by Borovsky) show that this plume can persist for hours, extending all the way from the ionosphere to the magnetopause.

Keeping HIV at Bay?

Preexposure prophylaxis involving daily doses of drugs can, with variable success rates, interrupt HIV transmission for individuals at high risk of acquiring HIV infection. However, one reason for the variability seen in the response to such drugs is a lack of adherence to the prescribed regimen. Andrews et al. (p. 1151) formulated a potent integrase inhibitor as a long-acting agent that protected macaques from repeated intrarectal challenges of simian HIV. Decay of plasma levels of drug were associated with increased susceptibility to infection after virus exposure. The drug levels required for a high degree of protection could potentially be achieved with quarterly injections in humans.

River Reorganization

CREDIT: SCOTT MCCOY/UNIVERSITY OF NEVADA, RENO

As rivers flow, they slowly transform the landscape. Their channels migrate, banks erode, and rivers can even flow backward if merged with another river. To understand how river basins balance erosional forces with regional tectonic uplift, Willett et al. (10.1126/science.1248765) analyzed maps of a proxy for river elevation and horizontal movement of river drainage divides across three large river systems in China, Taiwan, and the United States. Along with numerical modeling, the results demonstrate the degree to which these basins are at topographic equilibrium. The changing connectivity and topography of river networks influences how species migrate and how much material is delivered to larger bodies of water.

Immune Variation

It is difficult to determine the mechanistic consequences of context-dependent genetic variants, some of which may be related to disease (see the Perspective by Gregersen). Two studies now report on the effects of stimulating immunological monocytes and dendritic cells with proteins that can elicit a response to bacterial or viral infection and assess the functional links between genetic variants and profiles of gene expression. M. N. Lee et al. (10.1126/science.1246980) analyzed the expression of more than 400 genes, in dendritic cells from 534 healthy subjects, which revealed how expression quantitative trait loci (eQTLs) affect gene expression within the interferon-β and the Toll-like receptor 3 and 4 pathways. Fairfax et al. (10.1126/science.1246949) performed a genome-wide analysis to show that many eQTLs affected monocyte gene expression in a stimulus- or time-specific manner.

Plant Epigenetics

Quantitative trait loci (QTLs) are genetic regions associated with phenotypic traits that help to determine the underlying genetics controlling the magnitude of a specific trait. Cortijo et al. (p. 1145, published online 6 February; see the Perspective by Schmitz) identified epigenetic QTLs associated with differences in methylation marks (epiQTLs) controlling flowering time and root length in the model plant Arabidopsis. These epiQTLs were mapped in genetically identical lines that differ only in their methylation marks. A small number of QTLs were able to explain up to 90% of the heritable variation in these traits. Thus, in plants, the heritability of some complex traits can be determined by epigenetic variation.